Photovoltaic (PV) modules and related mounting hardware are well known and in widespread use. The most common mass-produced PV modules in use today include a laminated portion, or PV laminate, and a frame portion, and are designed specifically to convert light into electricity. The PV laminate portion is for encapsulating solar cells in a substantially flat, weather-tight envelope comprising a laminated construction of various layers including but not limited to glass, clear plastic, encapsulant material (like EVA), active photovoltaic material, interconnecting conductors between solar cells, and a protective backsheet (like PVF film). Photovoltaic laminates are commonly manufactured today in rectilinear shapes like squares, rectangles, triangles, and trapezoids and, due to their fragile nature, are usually completely enclosed by a permanent, substantially rigid, glued-on frame portion which holds and protects the delicate edges of the PV laminate portion and provides a means of attaching the PV laminate to other objects without damaging the PV laminate. The combination of the PV laminate portion and the glued-on frame portion is referred to herein as a PV module or framed PV module. The present invention relates to integral glued-on frames for standard PV laminates as are currently being produced, and to the associated mounting hardware which attaches to the integral frames for the purpose of securing the PV module to a roof or support structure.
Since PV cells are typically optimized to produce electricity most efficiently from direct sunlight, most PV modules are mounted outdoors on roofs or support structures. There are two primary methods utilized to reliably mount PV cells in the sun: (a) attach a standard framed PV module to a building, vehicle, or structure, or (b) integrate an unframed, PV laminate into a standard type of building material like a roofing product (shingle, tile, etc.), curtain wall, or a skylight framing system such that the PV laminate forms a part of the weather-tight skin of the building.
The latter approach is commonly referred to as “Building Integrated PV” and is not the subject of this invention. While there have been a number of recent developments in the field of building integrated photovoltaics, there are still very few installations because of their complex building design issues, higher costs, difficult ventilation issues (PV cells operate more efficiently with adequate air flow for cooling), problematic servicing issues (when a cell, laminate, or wiring connection fails), and inability to work well in retrofit applications.
Physical mounting issues associated with the installation of standard, framed photovoltaic modules include the following:
Alignment: Most photovoltaic systems are mounted on roofs and or structures which are not truly flat or straight despite the original design on paper (due to inherent deflection and flaws in materials). PV module alignment (in all three dimensions) is the biggest issue that photovoltaic installers face. The glass on photovoltaic modules heavily amplifies the normal dips and peaks that exist on roofs and structures. If the PV array is not straight, it is very noticeable from the ground. Typical variance is 2″ maximum in any one section of a roof, though over a large roof, it may sag by up to 4″. Alignment issues have typically been dealt with during installation by attaching multiple framed PV modules to several struts or channels and then attaching the struts or channels to separate foot-type pieces which include adjustable height provisions like slots or holes at different heights. Since this technique results in significantly less adjustability points than if the alignment features were built into the PV module frame, the result is that PV installers frequently spend hours just working on the alignment and generally have to eventually settle for an array which is only partially aligned and in many cases substantially non-planar.
Grounding: The 2002 National Electric Code Article 690.43 allows grounding modules by either a grounding conductor (as is typically done) or by making electrical contact with a metal rack or support structure. Given the importance of grounding for lightning protection and personnel safety, most respectable installers run large #6 ground wires to every module—a very time consuming and tedious task which still doesn't properly ground the array unless ground wires are also run to all struts and metal supports (hardly ever done because it requires threading each strut). Using the mounting structure as the ground is generally not done, primarily because it is somewhat vague in the code and installers don't know how to make lasting “electrical contact” on a structure exposed to the weather (for example, standard, self-tapping screws are not allowed). This is a major problem area because most photovoltaic arrays are not properly grounded.
Wiring: The most common wiring mistake that happens is a missed or improperly connected electrical connector between two modules (almost all photovoltaic modules now come with quick-connect, plug-type connectors for simplified and fast wiring). Even though the development of plug-type connectors have improved intermodule wiring, getting back into the middle of an array to physically reach the wiring and fix a problem can be a time-consuming process, particularly with some mounting systems. In many cases the entire row of PV modules plus all of the large ground wires plus wire strapping must be removed just to locate the problem area. Most roof mounted PV modules are mounted within 6″ of a roof surface and in the same plane, so if wiring is beneath the modules or inside the module frames, it is not easily accessible once installed.
Connecting to rafters: It is generally accepted that photovoltaic modules should be secured to the rafters, or other primary structural members (purlins, joists, etc.) for structural integrity and prevention of leaks, as opposed to screwing modules down to the sheathing. A single, typical aluminum framed PV module can expand and contract under normal temperature fluctuations by as much as 1/16″ and a whole 60′ long array by as much as 1″. If the array is only secured into the roof sheathing, then expansion and contraction over time will break the seal and create roof leaks. This issue is typically handled by use of additional struts or channels (since module edges or mounting holes rarely line up with rafters).
Collection of debris: If there are trees around, then debris (and sometimes small animals) will collect beneath modules. Some contractors prefer mounting modules higher to allow easy access for cleaning.
Water damming: Anything long and horizontal directly mounted right down on a roof is a potential leak site because water will dam up there. Roof mounted PV modules must be off of the roof, or building integrated PV s must be utilized.
Module temperature: Photovoltaic modules become less efficient the hotter they get. It is therefore required to provide some airflow beneath the modules if more efficient operation is desired. While airflow is not generally a problem on ground mounted structures and racks, roof mounted PV arrays generally perform much better when elevated off of the roof surface (as opposed to being mounted directly down on the roof surface).
Penetrations: Despite the incredible reliability of advanced roof sealants, PV contractors always want to minimize the number of penetrations that have to be drilled through the roofing surface since they are the ones who are liable for roof leaks. This is typically addressed by the use of additional struts or channels which serve to span multiple PV modules thereby minimizing the number of penetrations required.
Ease of installation: Though most people agree that PV systems provide the most environmentally sound method of producing electricity, the high capital cost of PV systems still prevents most people from being able to afford them.
Aesthetic mounting issues associated with the installation of photovoltaic modules include the following:
Module height: The generally agreed upon aesthetic that most homeowners and architects subscribe to assumes that photovoltaic modules should be either not viewable from the street, or if they are, they should be close to the roof and stand out as little as possible. Given this scenario, any ability to see beneath modules is not good, and insistence on optimum orientation (for example turning and/or tilting modules toward south when in the northern hemisphere on a roof or structure which does not face south) should be avoided. Generally speaking, the PV array should be as close to the same plane as the surface to which it is being mounted. Stated differently: the photovoltaic array should look like one large skylight. While some systems are capable of locating PV modules close to the roof, they generally require some offset from the roof and thus do not look like a skylight. This issue is slightly complicated because heating, debris, and water damming concerns all require an offset, while aesthetic concerns dictate a minimization of height.
Gaps between modules: The tighter the spacing, the better in order to minimize the view of the roof between PV modules and attain a skylight-like appearance.
Hiding other gear: Mounting hardware (like rails, hold-downs, or feet), junction boxes, conduit, wiring, and balance-of-system gear is unsightly, and should be neatly tucked away somewhere out of sight, especially from the street.
Module and frame color: Most homeowners and architects prefer black or dark bronze since these colors tend to draw the least amount of attention to themselves.
Numerous attempts have been made to address these problems, but most have been in the context of costly and cumbersome non-integral mounting hardware, such as improved PV strut systems with specialized “hold-down” pieces that connect the frame portions of PV modules to the strut or by utilizing building integrated techniques. Though the additional hardware developments have provided solutions to enough of the problems to become the dominant technique, many of the issues discussed remain unaddressed. Building integrated solutions also solve some of the problems but come with a host of new problems as discussed above.
Prior art examples include U.S. Pat. No. 6,672,018 to Shingleton which discloses a PV laminate mounting method and clip wherein a solar collector array is formed of a plurality of PV laminates mounted on a frame made of support beams which may be sheet metal channel members. A butyl tape or other glazing material is applied between the back laminate of the solar panel and the beam. Clips are used to clamp the panels to the support beams. The clips have an upper portion that is generally T-shaped in profile, and a retainer in the form of a channel nut or bar, with a threaded hole that receives a bolt or similar threaded fastener. The retainer biases against the inwardly directed flanges of the channel support beam. Electrical wires and mechanical fasteners are concealed within the support beams.
While this design does eliminate costly and unnecessary materials, it creates a new series of problems: fragile edges of the laminate are exposed and likely to break during normal-installation and/or roof maintenance, the system does not provide any means for vertical adjustability and will therefore include rows of PV laminates at differing heights which will compromise the aesthetic appeal, use of adhesive directly on the laminate means that removal of a single or multiple laminates may be difficult or impossible in some cases, thereby greatly reducing the maintenance capabilities of the system, and since PV systems are typically designed to last at least 30 years, the use of an adhesive which is exposed to the weather and under extreme daily temperature fluctuations is of questionable long term reliability.
U.S. Pat. No. 6,606,830 to Nagao et al. describes a building integrated photovoltaic roof including a roof base member provided on a partition wall which partitions a building into an indoor portion and an outdoor portion, a solar cell module provided on the roof base member, and electric wiring with one end portion being electrically connected with the solar cell module. The end portion of the electric wiring is drawn to the outside from between the roof base member and the solar cell module and at an outdoor-sided position than an indoor side face of the partition wall.
U.S. Pat. No. 6,465,724 to Garvison et al. teaches a photovoltaic module framing system with integral electrical raceways wherein a multi-purpose photovoltaic module framing system is provided which combines and integrates the framing system with the photovoltaic electrical system. The frame includes at least one rail which receives fasteners to directly mount the module on or to a roof, wall, rack, beam, or other structure. The frame has portions to space the PV module above a roof, so as to form a gap between the module and the roof to channel water, as well as to provide an air passage to cool the module. The frame includes portions that hold the PV laminate and for mechanically mounting the frame to a support structure. The PV modules are also overlapping interleaving side rails between intermediate PV modules and outboard PV modules. The overlapping, interleaving side rails can have a regular or inverted C-shaped or bracket shaped cross section with: (a) overlapping upper side flanges, which extend laterally outwardly from upper portions of the modules, (b) overlapping lower side flanges, which provide feet that extend laterally outward from lower portions of the modules, and (c) an intermediate side bight which provides a side crossbar that extends between and integrally connects the overlapping upper and lower side flanges. The bottom exterior surfaces of the feet can abut against and engage the shingles of an asphalt shingle roof. The multi-purpose frames also have integral electrical raceways which conceal and protect most electrical components and wires. The reliable frames are specially constructed and arranged to permit easy access to output wires and do not require junction boxes. Ground clips can be directly connected to the convenient framing system.
While this attempt does solve a number of the problems outlined, it has the following major faults which have significantly impeded adoption: (a) the lag bolts go through pre-defined holes which means that the lag bolts in most cases will have to be screwed into the sheathing, missing rafters and therefore causing roof leaks; (b) there is no vertical adjustability so the sides which abut each other will be not be level with each other in most cases (since roofs are not flat) dramatically diminishing the aesthetic appeal of the PV array; (c) design is not backwardly compatible with the common inward facing flange integral frame and thus requires contractors to completely re-tool and learn a totally different product which impedes adoption of the invention; (d) can't remove a module from the middle if it breaks without painstakingly removing the whole row; (e) it requires three different types of extrusions per PV module which means triple the cost for tooling to manufacture the unit as compared to a design with only one type of extrusion; and (f) design only allows for PV modules mounted in portrait orientation (long dimension of the module running perpendicular to the roof ridge), yet most roofs can actually fit more PV modules in landscape orientation since the long dimension of the module is now parallel with the long dimension of the roof (most roofs are longer side to side than they are from ridge to gutter). Regarding the maintenance issues, if you do have to remove modules for service, you have to literally rip up all of the now dried roof sealant and pull lag bolts out of the sheathing—a very time consuming process. Or worse yet, if a module or wiring connection is suspected to be faulty right after initial installation (the most likely time to discover a problem), then modules will have to be removed exposing wet sealant and causing a mess. To avoid the sealant problems mentioned above, the only option would be to use an inferior type of sealant like butyl tape which no experienced PV contractor would want to do because of roof leak liability.
U.S. Pat. No. 6,414,237 to Boer discloses solar collectors, articles for mounting solar modules, and methods of mounting solar modules, including a solar collector comprising at least one solar module; at least one solar module frame which supports the solar module; and at least one solar module bracket comprising a profile channel engagement hook, the profile channel engagement hook comprising a neck portion and a foot portion, the foot portion having a foot portion cross-sectional area in a first plane which is larger than a cross-sectional area of the neck portion in a second plane parallel to the first plane. There is also provided a profile channel attached to or integral with a support structure, the profile channel having at least one opening, the profile channel engagement hook engaging the opening such that the neck portion extends through the opening. There are also provided methods of making such solar collectors and methods of mounting such solar collectors on support structures.
U.S. Pat. No. 6,336,304 to Mimura et al. describes a building integrated photovoltaic roof in which an upper-end engaging portion of a downstream roof panel is seam jointed with a lower-end engaging portion of an upstream roof panel, wherein at least the lower-end engaging portion has flexural rigidity enough to disengage the seam joint.
U.S. Pat. No. 6,269,596 to Ohtsuka et al. teaches a building integrated photovoltaic roof member and mounting method thereof wherein roof members are those fixed to the roof, each roof member being a combination solar cell and roof member having a solar cell element and a metal reinforcing member, wherein a metal member is provided below the combination solar cell and roof member or a metal member is provided along an adjacent portion between adjacent combination solar cell and roof members, wherein the metal member is electrically conductive to metal reinforcing members of plural combination solar cell and roof members and wherein the metal member is electrically grounded. Provided based on this structure are the roof members easy to install and excellent in the external view and electric safety.
U.S. Pat. No. 6,242,685 to Mizukami et al. discloses a structure and method of installing photovoltaic modules wherein a photovoltaic module has a cathode and anode acting as electrodes for collecting an output power. When the photovoltaic module is installed on a roof of a building for example, the cathode is located at a position higher than the anode.
U.S. Pat. No. 4,636,577 to Peterpaul describes a building integrated photovoltaic module for directly mounting to a roof surface comprising a plurality of solar panels and a low profile, elongated frame including a generally flat, rectangular base having a plurality of substantially planar surfaces for supporting the under surfaces of the solar panels. The panels are removably sealed to the frames at the under surfaces thereof, rendering the upper surfaces fully free and unencumbered for receipt of incident solar radiation. The frame includes, integrally therewith, upstanding walls adjacent opposite edges of the panel supporting surfaces, defining raceway channels for concealed passage of electrical wires connected to the solar panels. The channels and walls have provision for overlapping interlocking with similarly fabricated frames for ease of installation, weather-proofing and high-density panel mounting.
U.S. Pat. No. 4,392,009 to Napoli teaches a solar power module comprising an array of solar cells arranged on a flat panel, the panel being supported by a substantially rigid, easily assembled frame comprising spaced apart side channels that each interlock with adjacent end channels to form a single photovoltaic module.
U.S. Pat. No. 4,336,413 to Tourneux discloses a building integrated photovoltaic generating panel easily adaptable to a roof. The panel is equipped with a peripheral frame formed by the assembly of straight light alloy shapes. The particular form of these shapes makes possible the laying of adjacent panels with overlapping of the edges of the latter similar to roof tiles.
U.S. Pat. No. 4,246,892 to Waiche describes a solar thermal energy collector panel, having an absorber plate and a frame within which the absorber plate is mounted. The absorber plate is comprised of a plurality of absorber plate sections each having interlocking structure formed along both of their lateral edges. This interlocking structure forms a tubular passage when the interlocking structure of the adjacent absorber plate sections are matingly locked together. An elongated tubing member whose external diameter is slightly larger than the internal diameter of the tubular passage is frictionally captured within each of the tubular passages. The absorber plate sections are formed of extruded metal and they have a plurality of corrugated surface portions that provide the absorber plate sections with greater surface exposure and improved absorption angles to the sun throughout the day. The thickness of the absorber plate sections is the greatest where the interlocking structure of the adjacent absorber plate sections are matingly locked together, thereby providing a greater mass for heat conduction transfer from the absorber plate sections to the elongated tubing member. The interlocking structure formed on the lateral edges of the absorber plate sections comprise a fin portion whose configuration is basically that of a cylindrical tube that has been cut in half longitudinally. A recess is formed adjacent one edge of the fin portion and a protrusion is formed adjacent the opposite edge of the fin portion. The frame has a back plate, side frame members, end frame members, and a glass top panel.
The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant's acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.
Furthermore, it is clear from the lack of prior art and number of problems which still remain unaddressed, that a definite need exists for a simple, cost-effective widely adaptable PV module mounting system which is integrated into the PV module frame design and which provides improved alignment capability, simplified and more reliable grounding, wiring which is hidden from view yet always accessible without removing a PV module, ability to always connect to the rafters, minimization of required penetrations in the roof, greater ease of installation, backward compatibility with inward facing flange framing systems, ability to connect PV module frame directly on top of a roof or mounting structure without the need for costly struts and hardware or expensive building integrated PV technologies, ability to remove any PV module in the array without having to remove others or pull out primary penetrating bolts, ability to easily add and remove optional items like debris screens and cosmetic flashings and caps, and improved appearance.